Extracelluar potassium ions play important roles in the selectivity of mutant KcsA channel

Potassium channels are exquisitely selective, allowing K⁺ to cross cell membranes while blocking other ions, such as Na⁺ and Cs⁺. It is now universally accepted that the selectivity filter is the functional unit that allows K⁺ channels to distinguish potassium and sodium ions. In this paper, we adopted the density functional theory and the Brownian dynamics to study the selectivity mechanism of KcsA^D-Ala77 in low and high [K⁺] conditions. The results suggest that the extracelluar potassium ions can change the conformation of the ion channels which can affect the interaction between the ions and the filter of ion channels. It is the interaction that determines the selectivity of potassium ions channels. The KcsA^D-Ala77 can permeate potassium and sodium ions in low [K⁺] conditions, but only permeate potassium ions in high [K⁺] conditions. The results are consistent with the experimental data. The results may demonstrate that the selectivity is a property of the channel structure, not only the consensus sequence of amino.